Fibrillation of natural fibres

Abstract

Fibrillation of certain cellulosic fibres has been widely studied, and fibrillation can be utilised to improve fabric performance, for example strength, absorbency, surface area together with handle and opacity. However, it believed that keratinous fibres such as wool have not been treated in this way. The invention seeks to provide a fibrillated keratinous fibre fabric and a method of fibrillating natural fibres. A textile fabric of keratinous fibre is disclosed characterised by the presence of fibrils, micro-fibrils and proto-fibrils. The fibrils may be further characterised as having diameters in the range 3 .mu.m to 5 .mu.m and by having lengths in the range 25 .mu.m to 60 .mu.m. Preferably, the fabric is a woven, knitted, non-woven or composite fabric. A method of treating natural fibres is also disclosed which comprises:- a pre-treatment to remove surface lipid materials or scales, e.g. using an oxidising agent; a treatment to remove or partially remove intercellular cement, e.g. using an enzyme; and the application of mechanical agitation under aqueous conditions, e.g. hydroentanglement, to complete fibrillation.

Description

[0001] This invention relates to a method for fibrillating natural fibres, and in particular relates to a method for fibrillating keratinous fibres such as wool and to a fibrillated product.

[0002] Fibrillation refers to the separation of wool fibres into finer elements, or fibrils, of smaller diameter. These maybe me macro-fibrils, proto-fibrils, or combinations thereof. Fibrillation of certain cellulosic fibres has been widely studied, and fibrillation can be utilised to improve fabric performance, for example strength, absorbency, surface area together with handle and opacity. However, it believed that keratinous fibres such as wool have not been treated in this way.

[0003] The invention seeks to provide a fibrillated keratinous fibre fabric and a method of fibrillating natural fibres.

[0004] According to the broadest aspect of the present invention there is provided a textile fabric of keratinous fibres characterised by the presence of fibrils, micro-fibrils and proto-fibrils.

[0005] The fibrils may be further characterised as having diameters in the range 3 .mu.m to 5 .mu.m and by having lengths in the range 25 .mu.m to 60 .mu.m.

[0006] Preferably, the fabric is a woven, knitted, non-woven or composite fabric.

[0007] The invention also provides a method of treating natural fibres which comprises:

[0008] a pre-treatment to remove surface lipid materials or scales;

[0009] a treatment to remove or partially remove intercellular cement; and

[0010] the application of mechanical agitation under aqueous conditions to complete fibrillation.

[0011] For preferential control of the fibre fibrillation, a pre-treatment to remove, modify or change the surface chemistry of keratin fibres is required.

[0012] The pre-treatment is necessary, with wool fibres, to remove surface lipid materials or scales which enclose the fibre core. This may be carried out with an oxidising agent, preferably using any of the oxidising agents widely known in connection with wool treatments (e.g. for imparting shrink resistant characteristics) such as Permonosulphuric Acid or its salt (PMS), Dichloroisocyanuric Acid or its salt (DCCA), Sodium Hypochlorite, Gaseous or liquid chlorine, peracetic acid, hydrogen peroxide, agqueous bromine, or, alternatively, electrical discharge (plasma) treatments, applied singly or in combination

[0013] The second stage of the process, namely removal of intercellular cement, may conveniently be carried out using an enzyme treatment, e.g. Papain, which is of vegetable origin and is successfully used by industry in other applications. Other alternatives include, without limitation, Scintillase, Esperase 8.0L, Durazyme 16.0L, Bactosol WO, Pronase, Alcalase, Savinase, Novozyme 735, Trypsin or Pepsin, separately or in combination. Reducing agents may be used in the enzyme bath, e.g. Dithionite, L-cysteine, or thioglycollice acid.

[0014] The mechanical agitation is preferably carried out under aqueous conditions. Energy may be introduced by the process known as "hydroentanglement" in which water jets are used to agitate the fibres and partially break them down into smaller, finer fibres, fibrils or micro fibrils. Other effective treatments may include laser etching, ultrasonic, plasma, mechanical raising or emerising. Mechanical treatments to the fabric may be carried out using either one method or a combination of such methods.

[0015] The process of the invention is particularly effective with keratinous fibres, for example wool, which normally cannot be fibrillated by chemical treatment or mechanical agitation alone. It has been found that the method of the present invention is successful in fibrillating keratinous fibres. Although primarily concerned with keratinous fibres, it has also been found that excellent results can be obtained when the method of the invention is applied to other natural fibres such as silk and natural cellulosic fibres. Although some fibrillation can be achieved without the process of the invention, particularly with cellulosics, it has been found that the method produces enhanced results.

[0016] Keratinous fibres which may be employed in the fabric and method of the invention include, but are not limited to, cashmere, camel, alpaca, mohair, and especially wool.

[0017] In order to facilitate the method of the invention, it is preferable that the fibres are initially scoured using a detergent or surfactant common in the textile field.

[0018] It is preferred that the chemical treatments of the first and second steps of the invention are applied using the "exhaustion" technique from long liquors.

[0019] It is preferred to use a reducing agent following the enzyme treatment in step 2 of the method. Suitable reducing agents are those widely known in textile processing such as sodium sulphite or sodium bisulphite.

[0020] The invention will be described further in the following examples, which are for illustrative purposes only. Reference is made to the accompanying drawings, in which:

[0021] FIG. 1 comprises four bar charts of frequency distribution of fibril diameter; and

[0022] FIG. 2 comprises four bar charts of frequency distribution of fibril length.

EXAMPLES

[0023] It was observed that fibre fibrillation can be achieved by treating samples with both chemical and mechanical processes in sequence. The chemical pre-treatment steps remove the surface lipid material or scales from the surface of the fibre and then break down the intercellular cement. The introduction of mechanical energy in the form of high pressure water jets further breaks down the intercellular cement resulting in the emergence of macrofibrils from the cortical cells. Fibrillation is clearly in evidence and has a marked effect on fabric handle.

[0024] 1. Wool Fibres

[0025] Fibrillation or separation of fibres into finer elements is achieved by treating samples with both chemical and mechanical processes in sequence.

[0026] 2. Cashmere

[0027] The fibre is pretreated with the same chemicals as used for wool. It is then subjected to mechanical energy, preferably hydroentanglement.

[0028] Examples of the chemical treatments that can be used are listed in table 1.

[0029] All samples were passed through a hydroentanglement machine using four injectors each operating at a fabric specific energy treatment of 100 bar water pressure (3.04 mj/kg).

1TABLE 1 Some Combined chemical and mechanical treatments used to obtain fibre fibrillation Chemicals Mechanical treatment Treatment Oxidising agent Enzyme agent Reducing agent Temperature (see table 2) A DCCA (6% owf) Papain (4% owf) + Na.sub.2SO.sub.3.7H.sub.2o/Na.sub.2S.sub.2O.sub.5 20.degree. C. Yes (NH.sub.4).sub.2SO.sub.4 10/10(% owf) B PSA (6% owf) Papain (3.5% owf) Na.sub.2SO.sub.3.7H.sub.2o/Na.sub.2S.sub.2- O.sub.5 20.degree. C. Yes 10/10(% owf) C DCCA (7% owf) Papain (1.5% owf) Na.sub.2SO.sub.3.7H.sub.2o/Na.sub.2S.sub.2O.sub.5 20.degree. C. Yes 10/10(% owf) D DCCA (5% owf) Papain (3.0% owf) Na.sub.2SO.sub.3.7H.sub.2o/Na.sub.2S.sub.2O.sub.5 20.degree. C. Yes 10/10(% owf)

[0030] There is no universally accepted standard method for the assessment of fibre fibrillation. Taylor (1993) introduced a Fibrillation Index, which is based on the use of a microscope to count the individual fibrils on the fibre surface. Obviously, this is a tedius method and because the fibrillation is not necessarily evenly distributed across the fabric, randomly selected fibres from a sample may produce biased results.

[0031] In order to evaluate fibre fibrillation an optical method was used based on image analysis of SEM images. In this method the light intensity level along a pixel line within the image is measured. The variation of light intensity along this line (which crosses the fibre perpendicular to its axis) can be used to obtain direct measurements of fibril diameter.

[0032] The results of treatments A-D (Table 1) are shown in FIG. 1. It was established that using treatment A, 50% of fibrils have a diameter of about 3 .mu.m and an average fibril diameter of 5 .mu.m. Applying treatment B results in an average fibril diameter of 4.8 .mu.m whereas, using treatment C a narrower range of fibril diameters with an average of 3.2 .mu.m was obtained. On the other hand, treatment D resulted in an apparently normal distribution with an average diameter of 4.4 .mu.m.

[0033] It should be noted that the skewed shape of some of the distributions may be due to limitations of the measuring system at 650.times. magnification. At this magnification, finer fibrils could not be clearly resolved by the microscope, and therefore measured by image analysis.

[0034] SEM images and image analysis were used to assess the length of fibrils detached from the parent fibre. The results of these measurements are shown in FIG. 2. Treatment A resulted in 50% of fibrils with a length of 45 .mu.m with a skewed distribution. The average length was 40 .mu.m. The average fibril length obtained using treatment B was 41 .mu.m. In comparison with the other treatments a shorter fibril length resulted from treatment C with an average of 31 .mu.m whereas, treatment D showed a wider range of fibril lengths with an average length of 51 .mu.m.

[0035] Chemical treatment alone can remove the wool scale structure but there is no concurrent fibrillation. The introduction of mechanical treatment alone in the form of high pressure water jets also resulted in no fibre fibrillation. On the other hand, when both chemical and mechanical treatments are applied in succession, significant fibre fibrillation can be obtained.

[0036] While not so-limited, it is believed that the fabric and method of the invention have two principal uses. Firstly, it may be used with woven, knitted, non-woven or composite fabrics to give a soft "fuzzy" fibrous surface or pile. Indeed, a very fine "peach skin" effect can be obtained. Patterning of the fabric surface appearance and texture can be achieved by localising the areas having fibrils, micro-fibrils and/or proto-fibrils, e.g. by selective application of the chemical treatment.

[0037] It can also be used to make non-woven fabrics. These, owing to the microfibrils, can be finer and/or denser than before. This means that less fibres are needed for a particular fabric, or, where the same number of fibres are employed, a denser fabric can be produced. One embodiment involves pre-treatment of the fibre before web formation followed by hydroentanglement, which is used both to consolidate the web and to split the fibres.

[0038] Consolidation and fibre splitting can be achieved either concurrently or sequentially in hydroentanglement in regard to keratinous fibres such as wool.

[0039] The degree of fibre pre-strain (stored strain) resulting from preparatory processes such as carding can also influence the degree of fibrillation or splitting of the fibres, when mechanical energy is subsequently applied. It may be beneficial to increase fibre strain by tensioning the fabric before or during application of the mechanical eery (e.g. by use of a fabric stenter machine). As referred to above, the invention is primarily useful in connection with keratinous fibres such as wool. It is also particularly useful with fibres of 21 microns diameter or above, particularly for coarser wools, such as British or New Zealand wools, where it produces a substantial beneficial effect.

Claims

1. A textile fabric of keratinous fibres characterised by the presence of fibrils, micro-fibrils and proto-fibrils.

2. A fabric as claimed in claim 1 wherein the fibrils are further characterised as having diameters in the range 3 .mu.m to 5 .mu.m and by having lengths in the range 25 .mu.m to 60 .mu.m.

3. A fabric as claimed in either of claims 1 or 2 wherein the fabric is a woven, knitted, non-woven or composite fabric.

4. A method of treating natural fibres which comprises: a pre-treatment to remove surface lipid materials or scales; a treatment to remove or partially remove intercellular cement; and the application of mechanical agitation to complete fibrillation.

5. A method as claimed in claim 4 wherein the first step is carried out with an oxidising agent.

6. A method as claimed in claim 5 wherein the oxidising agent is permonosulphuric acid or its salt (PMS), dichloroisocyanuric Acid or its salt (DCCA), or sodium hypochlorite.

7. A method as claimed in claim 4 or 5 wherein the first step is carried out using electrical discharge (plasma) treatments.

8. A method as claimed in any of claims 4 to 7 wherein he second stage of the process, namely removal of intercellular cement, is carried out using an enzyme treatment.

9. A method as claimed in claim 8 wherein the enzyme is Papain.

10. A method as claimed in any of claims 4 to 9 wherein the mechanical agitation is preferably carried out under aqueous conditions.

11. A method as claimed in any of claims 4 to 10 wherein energy is introduced by the process known as "hydroentanglement" in which water jets are used to agitate the fibres and partially break them down into smaller, finer fibres, fibrils or micro fibrils.

12. A method as claimed in any of claims 4 to 11 wherein energy is introduced may means including laser etching, ultrasonic, plasma, mechanical raising or emerising, separately or in combination.

13. A method as claimed in any of claims 4 to 12 wherein the fibres are keratinous fibres.

14. A method as claimed in claim 13 wherein the fibres are selected from cashmere, camel, alpaca, mohair, and especially wool.

15. A method as claimed in any of claims 4 to 14 wherein the fibres are initially scoured using a detergent or surfactant.

16. A method as claimed in any of claims 4 to 15 wherein the chemical treatments of the first and second steps are applied using the "exhaustion" technique from long liquors.

17. A method as claimed in any of claims 4 to 16 wherein a reducing agent is used following step two.

18. A method as claimed in claim 17 wherein the reducing agents is sodium sulphite or sodium bisulphite.